Neurotoxins which selectively alter the gating of voltage dependent sodium channels have been purified from the venoms of two species of scorpion, Centruroides sculpturatus and Leiurus quinquestriatus. Voltage clamp studies show that purified C. sculpturatus selectively alters the voltage dependence of sodium activation while L. quinquestriatus selectively delays sodium inactivation. Radiolabeled toxins have been prepared from both species which show saturable high affinity binding both to intact nerve membrane and to membrane proteins in detergent extracts. The goal of this work is to provide some biochemical information regarding the structure of the voltage dependent sodium channel. The current question being examined is whether these two physiologically distinct toxins bind to a common component or to molecularly distinct components. If the presumptive gating elements are distinct, the stoichiometry of those molecules in the membrane will be determined.